Unit dose cleaning products are preferred by many consumers for their ease of use and ability to prevent skin contact with irritating cleaning compositions. A unit dose cleaning product typically comprises a water-soluble pouch filled with a cleaning composition such as a granular detergent. The water-soluble pouch dissolves as a result of contact with water used in a cleaning cycle (e.g., an automatic dishwasher cleaning cycle) and consequently releases its dose(s) of the cleaning composition. The amount of cleaning composition within the water-soluble pouch is pre-measured and typically corresponds to the amount needed for a single cleaning cycle. Accordingly, the consumer is not required measure an appropriate amount of the cleaning composition prior to the cleaning cycle.
The exterior walls of the water-soluble pouch are typically very thin and thus susceptible to damage. To protect the water-soluble pouch prior to use, the water-soluble pouch is typically packaged within a protective container. One common type of protective container is a laminated barrier bag. Typically, multiple water-soluble pouches are packed, without separation, inside the laminated barrier bag. Therefore, if one of the water-soluble pouches breaks, the cleaning composition it leaks may compromise the integrity of the other water-soluble pouches inside the laminated barrier bag. Also, laminated barrier bags tend to be bulky and difficult to stack, and consequently require a substantial amount of shelf space. Furthermore, laminated barrier bags typically are made of a material that falls under Classification #7 of the Standard Classification System for Specifying Plastic Materials, such as oriented polypropylene (OPP), biaxially oriented polypropylene (BOPP), and/or polyethylene (PE). In general, such materials are difficult to recycle and thus undesirable from an environmental perspective.
Another type of protective container comprises first and second carrier sheets made of a relatively rigid and water-resistant material. The first carrier sheet includes a plurality of depressions in which the water-soluble pouches are positioned, and the second carrier sheet is sealed to the upper surface of the first carrier sheet to enclose each water-soluble pouch inside its corresponding depression. This type of packaging prevents the leaked contents of a damaged water-soluble pouch from affecting the other water-soluble pouches inside the container. Also, it may be easier to stack this type of container on a shelf than a laminated barrier bag.
One method of manufacturing such a container is described in U.S. Patent Application Publication No. 2004/0142131. The method involves simultaneously thermoforming a first water-soluble film and a first carrier sheet to create a plurality of internal holders in the first water-soluble film and a plurality of depressions in the first carrier sheet. An effect of thermoforming the first water-soluble film and the first carrier sheet at the same time is that the first water-soluble film acquires a temporary, or permanent, affinity for the first carrier sheet. As a result, the internal holders formed in the first water-soluble film retain their shape and are less likely to experience shrink-back prior to filling with the cleaning composition. Accordingly, it is possible to utilize the full volume of the internal holders at the filing stage.
After the internal holders have been filled with the cleaning composition, a second water-soluble film is sealed to the upper surface of the first water-soluble film, about the rims of the internal holders. This creates the plurality of water-soluble pouches. Typically, the first and second films are sealed together in an environment having an ambient pressure equal to, or substantially equal to, atmospheric pressure. As a result, the pressure inside the water-soluble pouches is equal to, or substantially equal to, atmospheric pressure, both during and after the sealing process. Accordingly, the water-soluble pouches do not experience a net external compressive force when placed in an environment having ambient pressure equal to atmospheric pressure.
Typically, the cleaning composition is loosely packed within the water-soluble pouches. The loose packing, combined with the relatively flexible exterior walls of the water-soluble pouches, renders the water-soluble pouches somewhat soft and, in some cases, unable to retain their shape when subjected to light abuse. Incomplete filling of the water-soluble pouches with the cleaning composition can also result in the water-soluble pouches being malleable. Although the water-soluble pouches may initially be attracted to the rigid carrier sheet as a result of being thermoformed simultaneously (as discussed in U.S. Patent Application Publication No. 2004/0142131), over time the affinity between the water-soluble pouches and the rigid carrier sheet may be lost. Consequently, by the time the consumer opens the container, the water-soluble pouches may no longer conform the shape of the depressions in the rigid carrier sheet. For example, the corners of the water-soluble pouch may become rounded even though the corners of the depression in the rigid carrier sheet are sharp and well-defined. The atmosphere surrounding the water-soluble pouches inside the container cannot be relied upon to compress and maintain the shape of the water-soluble pouches because, as noted above, a pressure differential typically does not exist between the interior of the water-soluble pouches and the surrounding atmosphere.
Consumers may perceive the soft and squishy feel of the water-soluble pouches as being indicative of low or inferior quality. Additionally, the inability of the water-soluble pouches to retain their shape limits their use in applications requiring specific geometric shapes.